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Freshwater Sponge

Freshwater sponges in Quantico creek

NPS photo

Importance

Freshwater sponges grow on sturdy submerged objects in clean streams, lakes, and rivers. Because they are sensitive to water conditions, their presence indicates high water quality and low levels of pollutants. Sponges are filter feeders. They obtain food from the flow of water through their bodies and from symbiotic algae. They also serve as food for ducks, crayfish, and a variety of macroinvertebrates including caddisflies, midges, lacewings, and spongillaflies. Of the phylum Porifera to which all sponges belong, only one family (Spongillidae) occurs in freshwaters of the United States, the rest are found in marine environments.

A close encounter with a sponge

NPS photo

Basics

Freshwater sponges are non-moving organisms that live at the bottom of water bodies. They are invertebrates (have no backbone) and do not have organs, but instead have specialized cells that help them filter water for food. The species Ephydatia muelleri found in this area is often green because of algae that lives in the structure of the sponge. For this reason, many people mistake freshwater sponges for algae, but sponges have a coarse texture, and are not slimy like algae. Freshwater sponges filter organic particles and bacterioplankton from water for food and also consume some products produced by their symbiotic algae. They can reproduce sexually, or asexually when small pieces are broken off and grow into new sponges. Sometimes, the sponge forms gemmules—tiny reproductive spheres that can overwinter and later hatch and form new sponges. Gemmules are generally formed in fall. Sponges can be identified to the species level only by examining the sponge's gemmule structure with a microscope.

A map of freshwater sponge locations

NPS photo

Sponges in the Washington, DC Area

Freshwater sponges (species unidentified) were reported in the mid-1970s in Wolf Trap Creek at Wolf Trap National Park for the Performing Arts, Mine Run Branch near George Washington Memorial Parkway, and Pimmit Run between George Washington Memorial Parkway and the Potomac River. No sponges have been observed in these spots since then. However, the freshwater sponge species Ephydatia muelleri (Mueller's freshwater sponge) was observed in Prince William Forest Park in South Fork Quantico Creek during the summer of 2007 by National Park Service personnel. Mueller's freshwater sponge (one of the most common sponges in North America) has since have been found in abundance in a second location in South Fork Quantico Creek and also in North Fork of Quantico Creek. Sponges are mainly found in shallow pools or light riffles. It is hoped that with renewed awareness of freshwater sponges in the area, more colonies will be identified. Please report any finds to visitor center staff at 703-221-7181.